DEFECT-BASED DESCRIPTION OF LITHIUM DIFFUSION INTO LITHIUM-NIOBATE

A defect chemistry approach is used to analyze the observed concentrat ion dependence of the lithium in-diffusion rate into lithium niobate. An ambipolar diffusion model is used where the lithium and niobium dif fusion rates are coupled and therefore cause an internal electric fiel d to develop during the diffusion process. Both lithium and niobium di ffusion are found to proceed via simple vacancy mechanisms. The intern al electric field forces the faster lithium diffusion to be reduced to a level consistent with the slower niobium diffusion process. This co upling gives a concentration dependence that matches the observed line ar increase in interdiffusion rate as the total cation vacancy concent ration decreases.